JP7256721B2 - Particle Beam Profile Detector and Particle Beam Therapy Apparatus - Google Patents

Description

The present invention relates to an apparatus for measuring the profile of a particle beam in a particle beam therapy apparatus that irradiates an affected area such as cancer with accelerated charged particles.

Particle beam therapy is a cancer treatment method that destroys cancer cells by irradiating charged particles (atomic nuclei of heavy particles such as protons and carbon) accelerated by a particle beam accelerator. A particle beam has the highest dose concentration near the end of its range. As a result, a large amount of energy can be released from the cancer-affected area, and damage to healthy tissue can be suppressed. On the other hand, particle beams emit a large amount of energy in a small irradiation area, so calculations are performed in advance to limit the irradiation area (target with cancer cells), and the limited irradiation area is irradiated with high precision. are required to do so.

In recent years, a spot scanning method, in which a thin particle beam is used to irradiate a target with a beam spot so as to cover it, has become a mainstream irradiation method. Also, a method of irradiating a target with particle beams from two or more directions is generally used. Therefore, from which angle, to which spot, and with what dose the particle beam should be irradiated is determined in advance by optimization calculation. The process of performing this optimization calculation is called treatment planning.

Also, in the treatment plan, in order to match the end of the range where the particle beam emits large energy with the target (cancer cell), what kind of dose distribution will the particle beam have in the patient's body in the direction of its central axis? Or should it be measured in advance? This measurement is generally performed by actually emitting a beam toward a phantom and measuring the dose distribution.

For example, Patent Literature 1 discloses a measurement method in which a container containing water is used as a phantom, a radiation measurement sensor is placed in the water in the container, and radiation is emitted toward the sensor.

In Patent Document 2, water containing phosphor is used as a phantom, the phantom is irradiated with a pencil-shaped beam of particle beams, and the light emitted by the beam passing through is photographed by a plurality of cameras arranged outside the phantom. Accordingly, a technique for measuring the dose distribution of a pencil beam is disclosed.

In Patent Document 3, focusing on the fact that weak light is generated when water is irradiated with a particle beam, a transparent container filled with water is used as a phantom, and the phantom is irradiated with radiation. Techniques for imaging weak light generated from positions through which radiation passes have been disclosed.

Patent Document 4 discloses a configuration in which a water phantom is inserted into the hollow of a solid phantom, a silver-activated phosphate glass plate is placed in the water phantom as a dose measuring means, and radiation is emitted. After irradiation, the silver-activated phosphate glass plate is removed from the water phantom and excited with ultraviolet light to emit fluorescence from the silver-activated phosphate glass at the radiation-irradiated locations. The radiation dose can be measured by reading this fluorescence with a reader.

Japanese Patent No. 3839687 Japanese Patent No. 5918865 (paragraph 0032) JP 2017-187286 A Japanese Patent No. 4384897

Proton beams and heavy particle beams are known as types of particle beams. In proton beams, protons do not split any further, so they fly relatively straight. A ray contains a plurality of protons and neutrons in the nucleus, and flies while partly splitting in the subject. For this reason, compared to proton beams, heavy ion beams have the characteristic of being more likely to spread in beam diameter as shown in Fig. 5(a). profile) with high accuracy is necessary for making a treatment plan.

Since the particle beam therapy system is a large device, it is completed by assembling the component parts at the installation site, and is handed over to the customer after a test run. It is desirable that the dose distribution of particle beams actually emitted from the apparatus is measured during the trial operation period and used for creating a treatment plan after operation. For this purpose, it is desirable to measure the dose distribution (beam profile) of the particle beam with high accuracy in a short time at least within the plane (inside the spot) perpendicular to the central axis of the particle beam at the installation location of the particle beam therapy system. be

However, when attempting to measure the beam profile by the technique described in Patent Document 1, the position of a small radiation measurement sensor is moved two-dimensionally by minute amounts, and the radiation (particle beam) is repeatedly irradiated, and the radiation is emitted one point at a time. The intensity needs to be measured (see Figure 3(a)). Therefore, there is a problem that it takes a long time to measure the beam profile.

On the other hand, the techniques described in Patent Documents 2 and 3 are methods of measuring the intensity of light emitted by a particle beam passing through an aqueous solution or water of a phosphor with a camera. In order to measure the (beam profile) as a light quantity distribution with a camera, it is necessary to arrange the optical axis of the camera and the central axis of the radiation to be aligned or parallel. At this time, the light that reaches the camera is the sum of the light emitted at each position through which the radiation of the aqueous solution of the phosphor or the water has passed. It is difficult to accurately measure the light intensity distribution (dose distribution) inside. In the technique of Patent Document 2, an aqueous phosphor solution is used as a phantom, but since there is an upper limit to the concentration of the phosphor that can be dissolved in water, the intensity of the fluorescence emitted by the passage of the particle beam must be increased to a certain extent or more. It is difficult. In addition, the technique of Patent Document 3 emits light from water itself, so the intensity of the light is weak. For this reason, there is also the problem that it is difficult to improve the accuracy of the dose distribution of radiation measured by light intensity beyond a certain level.

In the technique described in Patent Document 4, a silver-activated phosphate glass plate is placed at a position where it is desired to measure the dose distribution in water, and after irradiation with radiation, the silver-activated phosphate glass plate is taken out and irradiated with ultraviolet rays. Since it is necessary to excite by using a single measurement, labor and time are required for one measurement. Therefore, it is difficult to measure the beam profile of particle beams in a short period of time.

SUMMARY OF THE INVENTION An object of the present invention is to provide a detector that can easily measure the beam profile of a particle beam in water in a short time.

In order to achieve the above object, according to the present invention, there are provided a water tank, a plate-like phosphor arranged in the water tank and emitting fluorescence when irradiated with a particle beam, and a phosphor arranged outside the water tank, and a photodetector that receives the fluorescence that has passed through the water tank and detects the intensity distribution of the fluorescence on the light receiving surface.

ADVANTAGE OF THE INVENTION According to this invention, the detector which can measure the beam profile of the particle beam in water simply in a short time can be provided.

1 is a block diagram showing the overall structure of a particle beam therapy system according to an embodiment; FIG. 2 is a side view showing the configuration of the particle beam profile detector 100 of the embodiment; (a) Graph showing measurement points when dose distribution is measured in a conventional ion chamber, (b) Two-dimensional intensity distribution of fluorescence measured in the embodiment and its dose distribution on the DD' line. graph FIG. 4 is a side view showing the configuration of the particle beam profile detector of Embodiment 2; (a) Explanatory diagram showing the spread in the plane (xz plane) containing the central axis of the particle beam 21, (b) Graph showing the dose distribution of the central axis (z direction) of the particle beam 21, (c) of the particle beam Graph showing dose distribution in the direction perpendicular to the central axis (x direction) FIG. 4 is a block diagram showing the configuration of a treatment planning device of a particle beam therapy system of a particle beam irradiation system according to Embodiment 2; 6 is a flow chart showing the control operation of the particle beam profile detector of the second embodiment; Explanatory diagram of an example of a display screen showing recent and past particle beam dose distribution measurement results displayed on the display device in the particle beam therapy system of the second embodiment. The perspective view which shows a structure of the detector of Embodiment 3. (a) and (b) Explanatory drawing showing the measurement method of the comparative example

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below based on the drawings.

<<Embodiment 1>>
A particle beam therapy system equipped with the particle beam profile detector of this embodiment will be described. First, the overall structure of the particle beam therapy system will be described with reference to FIG.

As shown in FIG. 1, the particle beam therapy system includes a treatment table 15 for mounting a subject (treatment target), an accelerator 12 for accelerating particles, and a particle beam emitted from the accelerator 12 to the vicinity of the subject. It has a beam transport system 13 for transporting, and an irradiation nozzle 14 for irradiating the particle beam transported by the beam transport system 13 toward the subject. When measuring the dose distribution (beam profile) of the particle beam, a particle beam profile detector 100 having the structure shown in FIG. 2 is arranged on the treatment table 15 as shown in FIG.

In the particle beam therapy system of FIG. 1, an example of using a synchrotron accelerator to which the injector 11 is connected is shown as the accelerator 12, but it is of course possible to use an accelerator with other configurations such as a cyclotron accelerator. . A linear accelerator can be used as the injector 11 . In FIG. 1, the beam transport system 13 and the irradiation nozzle 14 are mounted on a rotating gantry (not shown) to rotate around the subject, but they may be fixed.

A beam controller 62 is connected to the injector 11, accelerator 12 and beam transport system 13 to control their operations. A beam profile detection controller 61 is connected to the particle beam profile detector 100 . A treatment planning device 63 is also connected to the beam profile detection control device 61 to create an optimum treatment plan using the measured beam profile (dose distribution) of the particle beam. During treatment of the subject, the beam control device 62 irradiates the subject with the particle beam according to the treatment plan created by the treatment planning device 63 .

Next, the configuration of the particle beam profile detector 100 will be explained using FIG.

The particle beam profile detector 100 includes a water tank 40 and a thin plate-like or film-like (hereinafter collectively referred to as plate-like) that is placed in the water tank 40 and emits fluorescence when irradiated with the particle beam 21. A phosphor 51 and a photodetector 55 arranged outside the water tank 40 are provided. The photodetector 55 receives the fluorescence 31 emitted from the phosphor 51 and passing through the water tank 40 to detect the intensity distribution of the fluorescence 31 on the light receiving surface.

In such a configuration, water 43 having a density close to that of the human body is put in the water tank 40, a plate-like phosphor 51 is placed in the water 43, and the particle beam 21 is irradiated from the irradiation nozzle 14, thereby irradiating the human body. A dose distribution of the particle beam 21 similar to that inside is produced in water. The phosphor 51 emits fluorescence with an intensity distribution corresponding to the dose distribution of the particle beam 21 at the position where the phosphor 51 is arranged. Therefore, of the emitted fluorescence, the fluorescence 31 that has passed through the water tank 40 is received by the photodetector 55, and the intensity distribution of the light on the light receiving surface is measured to obtain the dose distribution (beam profile) at the position of the phosphor 51. can be measured.

At this time, by arranging the plate-like phosphor 51 at a desired position on the central axis of the particle beam 21 and in a plane perpendicular to the central axis of the particle beam 21, the particle beam 21 can be measured by converting the dose distribution (beam profile) into the intensity distribution of fluorescence at once. Therefore, the beam profile can be measured in a shorter time than when detecting the dose while gradually shifting the position of the ion chamber.

In addition, the particle beam profile detector 100 of the present embodiment converts the dose distribution of the particle beam into the intensity distribution of the fluorescence in water, and passes the fluorescence through the water tank 40. Therefore, the particle beam is affected by the water tank 40. do not receive Therefore, the fluorescence accurately reflects the dose distribution of the particle beam. The fluorescence passes through a transparent water bath 40 that transmits fluorescence wavelengths and is detected by a photodetector 55 . Scattering and refraction of the fluorescence as it passes through the water bath 40 can be measured in advance and corrected for by preparing a calibration pattern that accounts for the effect.

Therefore, compared with the case where the particle beam 21 is passed through the water tank 40 and then irradiated onto the phosphor, the configuration of the present embodiment in which the fluorescent light is passed through the water tank 40 is less scattering of the particle beam that occurs when passing through the water tank 40. It is possible to accurately and quickly measure the dose distribution in water corresponding to the dose distribution in the human body without being affected by the

In addition, since the plate-like phosphor 51 has a higher concentration of the phosphor than an aqueous solution in which the phosphor is dissolved in water, it can emit fluorescence with a high intensity. Therefore, the photodetector 55 can accurately detect the fluorescence intensity distribution on the light receiving surface.

As described above, in this embodiment, the dose distribution of the particle beam emitted from the particle beam irradiation device can be easily measured in a desired direction in a short time.

Specifically, in the particle beam profile detector having the structure shown in FIG. The particle beam 21 is emitted from the irradiation nozzle 14 , passes through the water 43 stored in the water tank 40 in the depth direction, reaches the phosphor 51 on the bottom surface, and is irradiated to the phosphor 51 . The phosphor 51 has a structure that receives irradiation of the particle beam 21 from above and emits fluorescence toward at least the bottom member 41 of the water tank 40 .

As the plate-like phosphor 51, for example, one having a structure in which a phosphor particle layer is mounted on a plate-like support can be used. In this case, by arranging the plate-like support facing upward, with the phosphor particle layer facing the bottom member 41 of the water tank 40, the particle beam 21 passes through the support and reaches the phosphor particle layer. Then, the phosphor particle layer emits fluorescence toward the bottom member 41 . It is also possible to arrange the support so that the phosphor particle layer faces upward and the support faces the bottom member 41 . In this case, the support is made of a material that transmits the fluorescence emitted from the phosphor particle layer so that the fluorescence emitted from the phosphor particle layer is transmitted through the support and directed toward the bottom member 41 . use.

As the plate-like phosphor 51, it is possible to use a phosphor-containing ceramic, glass, or resin. In this case, since the phosphor 51 having self-supporting properties can be configured, the phosphor 51 can be configured without a support.

Also, the plate-like phosphor 51 may be of any type as long as it can convert radiation energy into light. The phosphor (fluorescent substance) as used herein refers to a substance that undergoes a transition to low energy while being excited by radiation and emitting fluorescence.

When the phosphor 51 has a structure in which a phosphor particle layer is mounted on a plate-like support, paper, for example, can be used as the support. It can be produced by applying a phosphor powder dissolved in a solvent to such a support and then drying it. Since the phosphor 51 having this configuration is thin, it can form a clear image on the light receiving surface of the photodetector 55, and has the advantage of emitting a large amount of light. However, in order to prevent the support and the phosphor particle layer from getting wet with water 43, it is desirable to perform waterproofing such as covering the whole with resin. Specifically, for example, both sides of the phosphor 51 are covered with a thin (several tens to several hundred μm) plastic film, and the edge is sealed with an adhesive or heat. Further, for example, it is conceivable that both sides of the phosphor 51 are waterproofed by vapor-depositing plastic. In any case, the waterproof layer made of plastic that covers the phosphor 51 is sufficiently thin compared to the thickness of the bottom member 41 of the water tank 40 (generally 2 to 5 cm thick), so that the particle beam 21 can pass through. The phenomenon that the particle beam 21 scatters is also very small.

On the other hand, when the plate-like phosphor 51 is made of ceramic, glass, or resin containing phosphor, for example, powder of the phosphor is dispersed in ceramic, glass, or plastic, and then molded. can be used. In these cases, the ceramic, glass, or resin can prevent water from reaching the phosphor, so that separate waterproofing may be omitted.

At least a region through which the fluorescent light 31 passes in the water tank 40 is made of a member that allows the fluorescent light 31 to pass therethrough. It is also desirable that this member has an antireflection structure for fluorescence. For example, in the configuration of FIG. 2, fluorescence 31 passes through bottom member 41 of water tank 40 . Therefore, in order to prevent light from being diffusely reflected by the bottom surface member 41 of the transparent water tank 40 and blurring the image on the photodetector 55, the bottom surface member 41 is provided with an anti-diffuse reflection structure (for example, a predetermined concave-convex structure). It is preferred to use glass. Also, a polarizing film that blocks reflected light may be attached to the resin or glass forming the bottom member 41 .

In addition, since the refraction angle of light passing through the bottom member 41 of the water tank 40 has wavelength dependence, the wavelength of the fluorescence 31 is selectively placed on the optical axis between the bottom member 41 and the photodetector 55. An optical filter may be provided to transmit the This allows only the fluorescence 31 to reach the photodetector 55 .

In addition, by installing an optical filter in front of the photodetector 55, the photodetector 55 detects the intensity of the fluorescence 31 reaching the photodetector 55 when measuring the beam profile of the large-dose particle beam 21. It can also be reduced to as much strength as possible.

The photodetector 55 is arranged at a position to detect the fluorescence 31 transmitted through the bottom member 41 of the water tank 40 . The photodetector 55 may be of any type as long as it can detect the light intensity distribution on the light receiving surface. For example, a CCD or CMOS camera, or a two-dimensional array of semiconductor photodetectors, etc. can be used. Also, the photodetector 55 may incorporate a lens.

As a result, the photodetector 55 can two-dimensionally detect the fluorescence intensity distribution in the plane perpendicular to the optical axis of the particle beam 21, as shown in the left diagram of FIG. 3(b). By correcting this fluorescence intensity distribution based on the previously determined relationship between the fluorescence intensity and the dose, the beam profile in the plane perpendicular to the optical axis of the particle beam 21 can be obtained two-dimensionally. . The diagram on the right side of FIG. 3(b) is a graph showing the dose distribution on the line D-D' shown in the diagram on the left side.

By using the particle beam profile detector 100 of the present embodiment, a two-dimensional beam profile can be obtained in one measurement. As a comparative example, as shown in FIG. Dose distribution can be measured more accurately in a short time than when measuring one by one.

In the first embodiment described above, the photodetector 55 is desirably placed in a place where the particle beam 21 does not hit it, in terms of durability. Therefore, for example, like the structure of FIG. 2, the photodetector 55 can be arranged not directly under the particle beam 21, but at a location slightly away from it. In this case, a deflection member (mirror) 52 that deflects the fluorescent light 31 and causes it to reach the photodetector 55 is arranged between the bottom member 41 of the water tank 40 and the photodetector 55 . The deflection member 52 is supported by a support structure 53 and is rotatable around a rotation shaft 54 .

Alternatively, the photodetector 55 may be arranged near the bottom member 41 of the water tank 40 and the upper portion of the photodetector 55 may be shielded with lead or the like.

In the structure of FIG. 2, the photodetector 55 is arranged inside the housing 50, and the housing 50 is preferably a darkroom structure except for the area through which the fluorescent light 31 passes. This can reduce the influence of the light from the environment in which the treatment table 15 is placed on the measurement results of the photodetector 55 . The water tank 40 is mounted on a housing 50 , and the housing 50 also functions as a support base for supporting the water tank 40 . The water tank 40 may have a structure that is detachable from the housing 50 .

Further, in order to form a clear image of the fluorescence 31 with little distortion on the light receiving surface of the photodetector 55, a structure 54 for supporting a mirror and adjusting its position and angle may be further arranged.

Moreover, the photodetector 55 is preferably mounted on the optical stage 156 in order to adjust the position and distance of the photodetector 55 .

In this embodiment, since the photodetector 55 is arranged outside the water tank 40, an image with a wide field of view and little distortion can be captured. Moreover, the photodetector 55 and its cable need not be waterproofed, and the particle beam profile detector 100 has high durability.

<<Embodiment 2>>
A particle beam profile detector 100 of Embodiment 2 will be described.

In the particle beam profile detector of Embodiment 1, since the phosphor 51 is arranged on the bottom surface of the water tank 40, the two-dimensional dose distribution (beam profile) in the plane orthogonal to the central axis of the particle beam is obtained. Although it can be measured, when measuring the beam profile at a plurality of different positions on the central axis of the particle beam, it is necessary to change the depth of the water in the water tank 40 and perform the measurement a plurality of times. Therefore, in the particle beam profile detector 100 of Embodiment 2, as shown in FIG. The distance from the water surface to the phosphor 51 can be changed without changing the depth.

Specifically, the phosphor drive unit 70 includes a track 72 provided in the depth direction on the inner wall of the water tank 40, and a drive unit 71 that holds the phosphor 51 parallel to the bottom surface and moves along the track 72. ,including. The track 72 was arranged parallel to the depth direction on the inner wall of the water tank 40, and the drive unit 71 included a motor, wheels, etc., and moved along the track 72 to keep the phosphor 51 parallel to the bottom surface. Move it up and down in the direction of the depth of the water.

In addition, between the bottom member 41 of the water tank 40 and the photodetector 55, a light collecting optical system 73 for collecting the fluorescence 31 transmitted through the bottom member 41 toward the light detector 55 and a light collecting optical system 73 and a drive unit 56, 74 for varying the distance from the photodetector 55 are further arranged. Specifically, the photodetector 55 is mounted on the driving section 56 and the condensing optical system 73 is mounted on the driving section 74 . A track 75 is arranged along the optical axis of the fluorescent light 31 between the photodetector 55 and the deflection member 52 . Both drive units 56 and 57 include motors, wheels, and the like, and can independently move on track 75 . With this mechanism, by adjusting the position of the condensing optical system 73 with respect to the photodetector 55, the fluorescence 31 can be imaged on the light receiving surface of the photodetector 55 even when the phosphor 51 moves up and down. .

A drive controller 61a is arranged in the beam profile detection controller 61 as shown in FIG. The drive control unit 61a controls the driving unit 70 of the phosphor 51, the driving unit 56 of the photodetector 55, and the driving unit 74 of the condensing optical system 73, so that according to the vertical movement of the phosphor 51, The position of the condensing optical system 73 with respect to the photodetector 55 is arranged at a predetermined position. As a result, the fluorescence 31 from the phosphor 51 is condensed by the condensing optical system 73 while the distance (depth) from the water surface is changed within a predetermined range by moving the phosphor 51 up and down. An image can always be formed on the light receiving surface of 55 .

Therefore, by moving the phosphor 51 to each depth of the central axis of the particle beam and measuring the two-dimensional distribution of the dose in the plane perpendicular to the central axis each time, the particle beam at a plurality of depths can be obtained. A two-dimensional dose distribution (beam profile) or a three-dimensional dose distribution can be obtained.

Further, by calculating the sum of the doses in the plane perpendicular to the central axis of the particle beam for each depth, the dose distribution in the central axis direction of the particle beam can be obtained as shown in FIG. 5(b).
Note that the drive control unit 61a may control the drive unit 56 of the photodetector 55 and the drive unit 74 of the condensing optical system 73 by position control that instructs the position, or by control that instructs the amount of movement. you can go In the case of position control, the drive units 56 and 74 are provided with a structure for detecting the position by measuring the distance to the reference object using a laser, for example. It is desirable to have a structure for measuring the amount of movement based on the number of revolutions of the motor or wheels, or a structure for estimating the amount of movement by reading marks on the track.

On the other hand, in the treatment planning device 63, as shown in FIG. 6, a treatment region setting unit 63a, an irradiation position optimization planning unit 63b, and a particle beam profile storage unit 63c are provided. The treatment region setting unit 63a displays a CT image or the like of the subject to the user, and sets the treatment region by, for example, accepting setting of a region to be treated within the subject on the image. The particle beam profile storage unit 63c receives and stores the measured particle beam profile from the particle beam profile detection control device 61 . The irradiation position optimization planning unit 63b creates an arrangement (treatment plan) of a plurality of spots to be irradiated with particle beams by optimization calculation in order to irradiate the entire treatment area with a particle beam of a predetermined dose or more.

<Beam profile measurement>
Here, the operation of each part when detecting the particle beam profile of the particle beam therapy system will be described.

A user or operator installs the particle beam profile detector 100 on the treatment table 15 in the treatment room 81 . At this time, the irradiation nozzle 14 and the particle beam profile detector 100 are aligned so that the particle beam irradiated from the irradiation nozzle 14 travels in the depth direction from the upper opening of the water tank 40 and reaches the phosphor 51 . do. The water tank 40 is filled with water to a predetermined depth so that the range in the depth direction for measuring the beam profile is submerged in the water. Here, the case where the measurement range in the depth direction (the axial direction of the particle beam) is predetermined will be described, but the measurement range may be received from the user via input means (not shown). .

A particle beam profile detection control device 61 and a treatment planning device 63 are arranged in the control room 82 . A beam profile detection control device (hereinafter simply referred to as a control device) 61 incorporates a memory and a CPU. The function to control each part and measure the beam profile is realized by software. However, the beam profile detection control device 61 of this embodiment can also be implemented partially or wholly by hardware. For example, a custom IC such as an ASIC (Application Specific Integrated Circuit) or a programmable IC such as an FPGA (Field-Programmable Gate Array) is used to configure the beam profile detection control device 61, and a circuit to realize its function. You can do the design.

First, the controller 61 instructs the drive controller 61a to place the phosphor 51 at a predetermined start position within a predetermined measurement range in the axial direction of the particle beam (step 701). The drive control unit 61a drives the driving unit 71 that holds the phosphor 51 to move it along the track 72, thereby arranging the phosphor 51 at a predetermined start position. At the same time, the drive control unit 61 a drives the drive units 56 and 74 to arrange the photodetector 55 and the light collecting optical system 73 at predetermined positions according to the position of the phosphor 51 .

The controller 61 instructs the beam controller 62 to irradiate the particle beam. The beam controller 62 controls the accelerator 12 and the like to irradiate the particle beam from the irradiation nozzle 14 (step 702). Beam irradiation is performed at high speed. Generally, it starts and ends in a few milliseconds to tens of milliseconds.

The particle beam 21 irradiates the phosphor 51 arranged so that the main plane is orthogonal to the axial direction of the particle beam 21, and the phosphor 51 has an intensity corresponding to the dose distribution (beam profile) on the main plane of the phosphor 51. Emit a distribution of fluorescence 31 . The fluorescence is transmitted through the bottom surface of the water tank 40 , deflected by the deflection member 52 , condensed by the condensing optical system 73 , and imaged on the light receiving surface of the photodetector 55 .

The photodetector 55 detects the fluorescence intensity distribution on the light receiving surface (step 703). At this time, the control device 61 controls the timing at which the photodetector 55 detects the intensity distribution. For example, when the photodetector 55 is a camera, the timing of imaging, for example, opening and closing the shutter with the control device 61 triggering an emission signal for instructing the beam control device 62 to irradiate the particle beam. Illumination and fluorescence detection can be synchronized.
The beam profile detection control device 61 receives the fluorescence intensity distribution detected by the photodetector 55, converts it into a particle beam dose distribution (beam profile) by calibrating it using a formula obtained in advance, and incorporates the stored in memory. Although it is known that the amount of light emitted by the phosphor 51 and the dose of the radiation 21 to be irradiated are close to a proportional relationship, the relationship (linearity) between the two is obtained and calibrated before measurement. In addition, refraction and the like when passing through the bottom plate of the fluorescent water tank 40 are also measured in advance to calibrate the beam profile.

The control device 61 instructs the drive control section 61a to move the position of the phosphor 51 by a predetermined depth (step 704). The drive control unit 61a controls the drive unit 71 to move the phosphor 51, and controls the drive units 56 and 74 so that the fluorescence 31 emitted by the fluorescence 51 is imaged on the light receiving surface of the photodetector. 55 and the condensing optical system 73 are also moved.

Then, returning to step 702, the controller 61 irradiates the particle beam, detects the intensity distribution at the current position of the phosphor 51, converts it into the dose distribution (beam profile) of the particle beam, and (steps 702-701). These operations are repeated until the phosphor 51 is arranged at all measurement positions in the measurement range (depth direction) (step 705). After measuring the dose distribution at all the measurement positions in the measurement range, the control device 61 stores the beam profile at each position stored in the memory in the particle beam profile storage section 63c of the treatment planning device 63 (step 706). ). The data stored in the particle beam profile storage unit 63c may be a set of two-dimensional beam profile data at each position in the depth direction, as shown in FIG. 5(c), or three-dimensional beam profile data. may be In addition, the control device 61 calculates the dose distribution in the axial direction of the particle beam from the two-dimensional beam profile at each position in the depth direction, as shown in FIG. store in

The control device 61 causes the display device 65 to display the stored two-dimensional beam profile or three-dimensional beam profile, as shown in FIG. Thereby, the user can confirm the current dose distribution of the particle beam by the display of the display device 65 . Alternatively, the particle beam profile storage unit 63c may have a database structure, and the controller 61 may store beam profiles in the particle beam profile storage unit 63c in time series. As a result, the time-series beam profile in the database can be displayed on the display device 65 as shown in FIG. 8, so that the user can also check changes in the time-series beam profile.

A procedure for creating a treatment plan by the treatment planning device 63 will be briefly described. The treatment region setting unit 63a of the treatment planning device 63 displays on the display device 65 or the like an image of the subject captured in advance by an X-ray CT device or the like. When the user sets the treatment area on the image via an input/output device (not shown), the treatment area setting unit 63a accepts the treatment area. The irradiation position optimization planning unit 63b receives the set treatment region from the treatment region setting unit 63a, and stores the dose distribution (beam profile) at each depth in the axial direction of the particle beam from the particle beam profile storage unit 63c. The particle beam irradiation position (spot position) for uniformly irradiating the entire treatment area with a dose equal to or greater than a predetermined value is determined by optimization calculation.

Thereby, the treatment planning device 63 can create a treatment plan. At this time, in the present embodiment, the measurement result of the beam profile of the particle beam actually irradiated is stored in the particle beam profile storage unit 63c. It is possible to accurately create a treatment plan for evenly irradiating the entire body with a dose equal to or greater than a predetermined value.

During actual treatment, the particle beam profile detector 100 is removed from the treatment table 15, the subject is mounted, the axial direction of the particle beam 21 is aligned with the subject, and the particle beam irradiation position set in the treatment plan is set. are irradiated with the particle beam 21 respectively.

In the present embodiment, a treatment plan can be created using the results of actual measurement of the particle beam profile in the particle beam therapy system after installation at the place of use, so irradiation accuracy can be improved.

<<Embodiment 3>>
The particle beam profile detector 100 of Embodiments 1 and 2 arranges the main plane of the phosphor 51 so as to be orthogonal to the central axis of the particle beam, and measures the dose distribution (beam profile) in that plane. However, the particle beam profile detector of Embodiment 3 has a configuration in which the phosphor 51 is arranged such that its main plane coincides with the central axis of the particle beam 21, as shown in FIG. The photodetector 55 is arranged on the side of the water tank 40 .

With such an arrangement, the phosphor 51 linearly emits fluorescence along the central axis of the particle beam 21 . The fluorescence light quantity distribution corresponds to the dose distribution of the particle beam 21 in the central axis direction. Fluorescence emitted from the phosphor 51 advances toward the side surface of the water tank 40 and passes through the side member 42 of the water tank 40 . Therefore, the photodetector 55 detects fluorescence transmitted through the side member 42 .

By calibrating the fluorescence intensity distribution in the axial direction of the particle beam 21 using the relationship between the fluorescence intensity and the dose obtained in advance, the dose distribution (beam profile) in the particle beam axial direction (see FIG. 5(b) ) can be obtained.

A three-dimensional beam profile of the particle beam 21 can be obtained by rotating the phosphor 51 in the axial direction of the particle beam 21 and obtaining the dose distribution for a plurality of rotation angles.

Since other configurations are the same as those of the first and second embodiments, description thereof is omitted.

In the above-described Embodiments 1 to 3, the phosphor 51 is arranged in water simulating the human body. It is also possible to position and measure the beam profile.

<<Comparative example>>
As a comparative example, the phosphor 51 is arranged outside the bottom member 41 and the side member 42 of the water tank 40, and the other configuration is the same as that of the first embodiment. Consider.

When the phosphor is arranged outside the water tank 40 , the particle beam 21 reaches the phosphor after passing through the water and the bottom member or the side member of the water tank 40 . For example, as shown in FIG. 10(a), when a phosphor is placed on the lower surface of the bottom member 41 (1 to 2 cm) of a water tank 40 with a water depth of 20 cm, the particle beam 21 reaching the phosphor is 20 cm deep. After being gradually scattered by water, the dose distribution is further scattered by the bottom member 41 of the water tank 40 . Therefore, since the phosphor 51 converts the dose distribution including the scattering by the bottom member 41 of the water tank 40 into fluorescence, the detection accuracy of the dose distribution is lowered.

In order to remove the influence of scattering by the water tank 40, if the thickness of the bottom member 41 of the water tank 40 is converted into a water equivalent thickness and the amount of water is reduced by that amount, the ranges of the particle beams can be matched. However, the influence of scattering by the water tank 40 cannot be eliminated. For example, when the range loss (thickness of the material passing through [g/cm ² ]) of the particle beam due to the bottom member 41 of the water tank 40 of 2 cm is equivalent to 2.2 cm of water, the depth of the water is set to 17.8 cm. Thus, the energy loss of the particle beam passing through 17.8 cm of water and the bottom member 41 of the water tank 40 of 2 cm can be matched with the energy loss of the particle beam passing through 20 cm of water. However, even with this adjustment of water depth, the degree of scattering is different. This is because the degree of scattering of particle beams depends on the elements that compose the substance, and the heavier atoms are more likely to be scattered. Therefore, the influence of particle beam scattering by the water tank 40 made of glass or resin cannot be canceled by adjusting the depth of the water.

On the other hand, in order to eliminate the influence of particle beam scattering by the water tank 40, as shown in FIG. After that, the particle beam 21 scattered by the water and the water tank 40 is measured by the phosphor 51, and the difference between the two is obtained. It is also possible to ask for However, the easiness of scattering of particle beams in matter depends on the energy, with high-energy beams scattering less and low-energy beams scattering significantly. Therefore, in the above measurement method in which the energy of the particle beam 21 when reaching the bottom member 41 of the water tank 40 differs depending on the presence or absence of water, the degree of scattering in the water tank 40 varies depending on the presence or absence of water. The degree of scattering of the particle beam 21 by water alone cannot be determined.

It is also conceivable to reduce the influence by thinning the bottom member 41 and the wall member of the water tank 40, but it is necessary to maintain the function of supporting without bending even when subjected to the water pressure of 30 cm deep water. It is difficult to reduce the thickness beyond a certain level.

From the above, the particle beam profile detector having the configuration of the comparative example in which the phosphor 51 is arranged outside the bottom member 41 and the side member of the water tank 40 can eliminate the influence of scattering of the particle beam 21 by the water tank 40. is difficult. Therefore, the particle beam profile detector of the comparative example has lower measurement accuracy of the dose distribution of the particle beam than the particle beam profile detectors 100 of the first to third embodiments.

1: Particle beam therapy device 11: Linear accelerator used as injector 12: Synchrotron accelerator 13: Beam transport system 14: Irradiation nozzle 15: Treatment table 21: Particle beam 40: Water tank 41: Water tank bottom member 42: Water tank side Member 43: Water 50: Housing 51: Phosphor 52: Deflecting member 53: Support structure 54: Rotating shaft 55: Photodetector 56: Driving unit 61: Beam profile detection control device 61a: Driving control unit 62: Beam control device 63: Treatment planning device 73: Condensing optical system 74: Driving unit 100: Particle beam profile detector 156: Optical stage

Claims (8)

a water tank having an upper opening, in which water is stored up to a predetermined depth ;
A plate-like phosphor that is arranged in the water tank parallel to the bottom surface of the water tank and emits fluorescence toward at least the bottom surface of the water tank when irradiated with a particle beam traveling in the depth direction from the upper opening of the water tank. and,
a first track provided along the depth direction on the inner wall of the water tank;
a phosphor driver that holds the phosphor and moves along the first track to change the distance from the water surface of the water tank to the phosphor;
a deflecting member disposed in a space below the bottom surface member of the water tank for deflecting fluorescence transmitted through the bottom surface member among fluorescence emitted by the phosphor upon being irradiated with the particle beam;
a photodetector arranged at a position where the fluorescent light deflected by the deflection member reaches;
a condensing optical system disposed between the photodetector and the deflection member for condensing the fluorescence;
a second track arranged parallel to the optical axis of the deflected fluorescent light between the photodetector and the deflection member;
a photodetector driving unit mounted with the photodetector and moving on the second track;
a condensing optical system driving unit mounted with the condensing optical system and moving on the second orbit;
a drive control unit that controls the phosphor drive unit, the photodetector drive unit, and the condensing optical system drive unit;
The drive control unit sets the distance of the phosphor from the water surface by operating the phosphor drive unit, and operates the photodetector drive unit and the condensing optical system drive unit. and disposing the condensing optical system and the photodetector at respective predetermined positions according to the position of the phosphor, condensing the fluorescence deflected by the deflection member with the condensing optical system, Form an image on the light receiving surface of the photodetector
A particle beam profile detector characterized by: 2. A particle beam profile detector according to claim 1, wherein said plate-like phosphor has a structure in which a phosphor particle layer is mounted on a plate-like support. vessel. 2. A particle beam profile detector according to claim 1, wherein said plate-like phosphor is made of ceramic, glass, or resin containing phosphor. vessel. 2. The particle beam profile detector according to claim 1, wherein a region of said water tank through which said fluorescence passes is composed of a member that transmits said fluorescence and has an antireflection structure for said fluorescence. A particle beam profile detector, characterized in that: 5. A particle beam profile detector according to claim 4 , wherein said antireflection structure is a concavo-convex structure provided on said member or a polarizing film attached to said member. beam profile detector. 2. The particle beam profile detector according to claim 1 , wherein an optical filter selectively transmitting fluorescent wavelengths is arranged between said bottom member of said water tank and said photodetector. A particle beam profile detector characterized by: A treatment table for mounting a treatment target, an accelerator that accelerates particles and emits a particle beam, an irradiation nozzle that irradiates the particle beam toward the treatment target, and the particle beam that is mounted on the treatment table. and a particle beam profile detector that measures the dose distribution of
A particle beam therapy system, wherein the particle beam profile detector is the particle beam profile detector according to any one of claims 1 to 6 . The particle beam therapy system according to claim 7 , further comprising a beam profile storage unit and an irradiation position optimization planning unit,
The particle beam profile detector measures a dose distribution in at least a plane perpendicular to the central axis of the particle beam and stores the measurement results in the beam profile storage unit;
The irradiation position optimization planning unit reads the dose distribution from the beam profile storage unit, and uses the dose distribution to determine a plurality of positions of the treatment target to be irradiated with the particle beam. Particle therapy equipment.

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